1. Field of the Invention
The present invention relates generally to a system and method for superplastic forming a workpiece; and, more specifically, to an automated system including a plurality of modules forming a superplastic forming cell.
2. Description of Related Art
Superplastic forming (SPF) takes advantage of a material's superplasticity or ability to be strained past its rupture point under certain elevated temperature conditions. Superplasticity in metals is defined by very high tensile elongations, ranging from two hundred to several thousand percent. Superplasticity is the ability of certain materials to undergo extreme elongation at the proper temperature and strain rate. SPF is a process used to produce parts that are difficult to form using conventional fabrication techniques.
SPF typically includes the steps of heating a sheet of material to a point of superplasticity, clamping the material within a sealed die and then using inert gas pressure applied to one side of the sheet of material to force the material to stretch and take the shape of the die cavity. Accordingly, SPF takes advantage of certain material characteristics, specifically increased elongation at higher temperatures or the ability to stretch a material by several times its initial length without breaking.
Standard SPF applications have advantages over conventional stamping techniques, including increased forming strains, reduced spring back and low tooling costs; however, they have disadvantages in that they are limited to low volumes as they normally require relatively long forming cycle times. Specifically, a conventional SPF processes used to manufacture a complex part can require a forming cycle time as high as 30 minutes.
Further, conventional SPF systems require that the forming die is cooled prior to removal. Once cooled the die is removed a new room temperature die is inserted into the press. Before production can resume, the new room temperature die must be heated to suitable SPF temperature. This causes a significant loss of production time and cooling down and heating up of the dies. Cool down and heat up can take anywhere from 24 to 48 hours each.
Reduced cycle times are necessary in order to use SPF for the high production requirements of the automotive industry. Accordingly, there is a need for a superplastic forming system that decreases cycle time and correspondingly increases production volume.